Genetics, molecular biology and biochemistry all depend on evolution, and they provide observations on a micro scale that correlate with the macro-scale observations made by other fields. (For example, species can be grouped into categories based on their physical appearance, and gene sequences can be grouped into categories based on similarity with other sequences. When these separate observations are considered together, there is a very good correlation between the category a species is placed in by its appearance and by its gene sequences.)
Here is a list of partial gene sequences for cytochrome c (one of the last steps in the process of extracting useful energy from carbohydrates and other nutrients) for a few species:
Molecular homology of cytochrome c
1 6 10 14 17 18 20
Human Gly Asp Val Glu Lys Gly Lys Lys Ile Phe Ile Met Lys Cys Ser Gln Cys His Thr Val Glu Lys
Pig - - - - - - - - - - Val Gln - - Ala - - - - - - -
Chicken - - Ile - - - - - - - Val Gln - - - - - - - - - -
Dogfish - - - - - - - - Val - Val Gln - - Ala - - - - - - Asn
Drosophila <<< - - - - - - - - Leu Val Gln Arg Ala - - - - - - Ala
Wheat <<< - Asn Pro Asp Ala - Ala - - - Lys Thr - - Ala - - - - - Asp Ala
Yeast <<< - Ser Ala Lys - - Ala Thr Leu - Lys Thr Arg - Glu Leu - - - - - -
Note how there are some changes in this sequences – but that the closely related organisms have very similar sequences. Though these are not shown, human cytochrome c is identical to that of chimpanzees, and differs in only one place from that of rhesus monkeys. The human sequence and yeast sequence (if the full sequences are compared) differ in 44 places, but in some positions are identical and have remained so over hundreds of millions of years of divergent evolution. This suggests that humans, chimpanzees, rhesus monkeys, and brewer’s yeast evolved from a common ancestor. (Note that this is not compatible with Genesis-type creationism, with separate creation events for humans, animals and plants.) It also suggests that, for example, humans and chimpanzees have a common ancestor, and that pigs and chickens have a common ancestor, and that wheat and yeast have a more recent common ancestor than do wheat and humans. Finally, it suggests that evolution occurs by progressive mutation in the genetic material of species. This is enough of an observation to make by itself, but when it correlates with other observations made independently, one begins to establish a very firm basis of evidence that evolution – by some mechanism which is still not conclusively known – did happen in some form.
(A creationist website attacks the cytochrome c sequences as not providing evidence for evolution by saying that no intermediate sequences are found. This is not really true; for one, it is a single gene sequence out of tens or hundreds of thousands that might be compared. (Some gene sequences mutate much more quickly than others. Some are very different between, say, humans and chimpanzees. Some have passed down almost unchanged from bacteria.) Some intermediate sequences may be ignored because they do not fit a creationist’s conclusions. Finally, intermediate sequences are far more difficult to find than sequences that clearly belong to a given category, because the intermediate organisms are largely extinct.)
Without evolution – without assuming that these different sequences had come about by gradual change as organisms diverged from common ancestors – these differences are very difficult to explain. In fact, they can probably be explained only by invoking the supernatural, an idea for which there is no evidence. Consider a scientific idea that does not conflict directly with religious thought – friction, for example. If we had a set of mathematical observations that suggested that interactions between a moving object and the surface on which it moved constituted a force opposite to the direction of motion of the object, would we ever decide that this cannot possibly occur by electrostatic repulsion, and that there must therefore be tiny demons that fly to every moving object and push on it to slow it down? It’s not merely that biology becomes very difficult to understand without evolution – it’s that biology without evolution requires the invocation of ideas that are wholly alien to science, ideas that are never demanded of fields that do not make certain religionists uncomfortable.